1. Field of the Invention
This invention relates to a method of and an apparatus for controlling ignition timing in an internal combustion engine, more specifically to a method of and an apparatus for controlling ignition timing in an internal combustion engine wherein the maximum value of ignition angle retardation at occurrence of knocking and the maximum angle of ignition advance after knocking has been avoided are varied depending on the operating condition of the engine.
2. Description of the Prior Art
In controlling ignition timing in an internal combustion engine, it is a common conventional practice to detect when knocking begins and then compensate the basic ignition timing to cause the knocking to stop. One example of such a practice is disclosed in Japanese Patent Publication No. 59(1984)-48308. In such a practice, the maximum amount of compensation is not changed over the whole range of engine operating conditions.
In an internal combustion engine, the knocking limit (the maximum angle of ignition advance at which knocking can be suppressed) intrinsically varies with the operating condition and operating environment of the engine. Naturally, the relationship between the knocking limit and the MBT (Minimum advance for Best Torque) also varies depending on the engine operating condition and environment. In the prior art, however, since the maximum amount of compensation is fixed over the full range of engine operating conditions, sometimes the amount of retarding compensation at the time knocking occurs is greater than necessary and also sometimes the amount of counter-compensation carried out in the direction of advance after knocking has been avoided results in an ignition timing that is still unnecessarily retarded than MTB. As a result, it has not been possible to obtain the full potential power of the engine.